The present invention relates to a method and apparatus for simulation, in particular, it relates to a method and apparatus for simulation for computing and displaying sound ray paths transmitted into sea-water in a sonar system.
Sonar (Sound Navigation and Ranging) has been used for locating schools of fish, detecting enemy submarines and navigating ships. There are two kinds of sonars, active sonar and passive sonar. The former transmits ultrasonic waves into sea-water and finds the direction and distance of an object from which wave is reflected by the propagation time and direction of the ultrasonic wave, while the latter finds them from the sound waves which are radiated by the object itself.
A sonar is, generally, designed on the premise that sound waves propagate straight in sea-water. However, sound waves in sea-water actually do not propagate straight but rather, curve because of the temperature and pressure distribution in sea-water. Accordingly, there appears some areas in which an object cannot be found.
Sound ray paths in sea-water have long been manually computed with a calculating table, however, this method is extremely troublesome and time consuming. Accordingly, an automatic sound ray path analyzer has been developed. The prior sound ray path analyzer, which is a special purpose analog computer, calculates the sound ray path of a sonar system from the information of temperature and depth provided by a B/T (Bathy-Thermograph) and displays the sound ray path on a screen of a cathode-ray tube or a pen-type X-Y recorder.
U.S. Pat. No. 3,832,537, owned by the present assignee, is an example of a prior analog computer type sound ray path analyzer.
However, said prior analog computer type sound ray path analyzer has the disadvantage that the calculation error in a divider is very large when a denominator is relatively small.
In order to overcome the above disadvantage, a completely digitalized ray path analyzer has been proposed, which however, has the disadvantage that it takes a very long time to solve a differential equation which is a major step in analyzing the ray path.